Random changes in allele frequencies in a population over time, especially pronounced in small populations. These changes occur by chance rather than natural selection and can lead to the loss of genetic variation.
From Greek 'genetikos' meaning 'of birth or origin' and 'drift' from Old Norse 'drift' meaning 'snowdrift' or movement. The term emerged in population genetics in the 1930s when Sewall Wright described how allele frequencies can 'drift' randomly like particles in Brownian motion.
Genetic drift is like flipping a coin - even if the coin is fair, you might get 7 heads and 3 tails in 10 flips just by chance! In small populations, these random 'bad luck' events can permanently eliminate beneficial genes, which is why conservation biologists worry so much about endangered species with tiny populations.
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